Our work and that of others strongly suggests that endogenous processes rather than exogenous mutagens in the environment mediate most germline mutations. Endogenous processes may also produce most of the mutations associated with certain types of cancer. However, non-dividing cells such as neurons, are no susceptible to cancer. Does spontaneous somatic mutation have any important consequences in these tissues? The long-term objective of this project is to test the hypothesis that cell death due to increased-spontaneous somatic mutation is an important substrate for neurodegenerative disorders by using a newly developed transgenic mouse mutation detection system (Big Blue (TM)). Big Blue mice carry the E. coli lacI gene within a lambda phage sequence which is integrated into the mouse genome. Mutations in the lacI gene can be isolated from mouse genomic DNA by incubation with lambda packaging extract and infection of E. coli. Mutations that inactivate the lacI gene produce blue plaques which can be isolated and analyzed. With this system, mutation frequencies and patterns will be determined for five regions of the brain and compared wi mutation frequencies and patterns of other somatic and germline tissues. The specific aims of the project are: 1) Determine if tissue/cell type, gender, age, or mitotic activity affect the pattern of mutation in mouse. 2) Determine if different regions of the brain have different patterns of mutation. 3) Determine the pattern of mutation in transgenic mice with defects in DNA repair. 4) Determine the pattern of mutation in transgenic mice with overexpressed mutated and norma superoxide dismutase 1. 5)Determine the effects of phage integration site and rodent species on the pattern of mutation.